In theory reducing the number of pixels will result in less noise in the images and also reduce the amount of blurring you get from camera shake. But that does depend somewhat on how the camera steps down the number of pixels generated.

The ISO is purely the sensitivity of the sensor, when you up the ISO the camera tries harder to extra data from the sensor. This allows you to use slower shutter speeds without camera shake but at the same time increases noise in the picture.

"Can I simply force it to do 100 with no ill effects?"

No. Locking it at 100 when the camera wants to increase it will reduce the noise in your photos, but the trade off is that the shutter speeds will be longer and therefore more camera shake.

If you want to keep the noise down but avoid camera shake in low light on a compact camera then you have three options:

- put it on a tripod (or rested on something) and lower the ISO
- use the flash
- buy a proper camera

Photography is always a balance of compromises, turning something up always means turning something else down.